1. Field of the Invention
The present invention relates to a lens frame into which two or more lenses are inserted, a lens assembly equipped with the lens frame, and an image-taking apparatus provided with the lens assembly.
2. Description of the Related Art
In recent years, automobiles have been provided with cameras. Meanwhile, nowadays, automobiles are equipped with display screens thanks to the widespread use of car navigation systems. Therefore, many of cameras installed in automobiles can display the state of a blind spot for a driver on a display screen provided in front of the driver's seat.
Incidentally, automobiles may be left outdoors in hot summer and in freezing winter and therefore, a camera installed in an automobile is required to operate properly over an extremely wide range of temperatures. In order to guarantee the proper operation of a vehicle-mounted camera, a lens assembly employed in such a camera needs to be not only lightweight and robust as generally required, but also resistant to stretching and shrinking with temperature for the purpose of preventing the occurrence of a blur due to a change in temperature. To meet these needs, ceramic barrels have been devised (see, for example, Japanese Patent Application Publications No. 2006-284991 and No. 2006-292927). Also, the inventors of the present application have proposed to apply porous ceramic to an optical component (see, for example, Japanese Patent Application Publication No. 2007-238430). The porosity of the porous body described in the specification of Japanese Patent Application Publication No. 2007-238430 is equal to or more than 10%.
Further, for instance, Japanese Patent Application Publication No. 2007-279557 describes a lens assembly having such a structure that lenses and spacing rings are inserted into a lens barrel through the front opening of the lens barrel, and a pressing ring is screwed on a front part of the lens barrel, thereby fixing the lenses to the lens barrel. A structure in which a porous ceramic barrel is applied to the structure of Japanese Patent Application Publication No. 2007-279557 will be described.
FIG. 1 is a diagram that illustrates an example of the structure of a lens assembly provided with a lens frame made of porous ceramic.
A lens assembly 1 illustrated in FIG. 1 is provided with a barrel 10, and the barrel (lens frame) 10 has a hollow part 100 having an object-side opening 101 and an image-forming-side opening 102. Formed on an object-side periphery of the barrel 10 is a male thread SR1. From the object-side opening 101, lenses L1 trough L4 and spacing rings SP1 through SP3 are inserted while being aligned along the optical axis. These elements L1 through L4 and SP1 through SP3 may be collectively referred to as optical members. In this example, as shown in FIG. 1, the lenses L1 trough L4 and the spacing rings SP1 through SP3 are alternately disposed and sequentially inserted into the hollow part 100 of the lens barrel 10.
Furthermore, the lens assembly 1 illustrated in FIG. 1 is provided with a pressing ring 11 that fixes the optical members L1 through L4 and SP1 through SP3 inserted into the hollow part 100 of the barrel 10, by pressing these optical members from the side where the object-side opening 101 is formed. The pressing ring 11 has: a mounting opening 110 into which an object-side part of the barrel 10 is inserted; and an optical opening 111 for making a central part of the lens L1 exposed. Among the optical members inserted into the barrel, the lens L1 is the one disposed at the position closest to the object. Formed on an inner wall on a mounting opening side of the pressing ring 11 is a female thread SR2 in which the male thread SR1 is engaged. When the male thread SR1 is engaged in the female thread SR2, the edge of an object-side surface of the lens L1 disposed at the position closest to the object on the object side is pressed by the pressing ring 11.
The lens assembly 1 shown in FIG. 1 is assembled by using the pressing ring 11 that presses the lenses L1 trough L4 and the spacing rings SP1 through SP3 in the barrel 10 toward the image-forming-side opening.
When the lens assembly 1 assembled in this way is installed in an automobile, the strength of the barrel 10 made of porous ceramic comes into play, making it possible to sufficiently deliver predetermined performance.
In the lens assembly with the structure described above, the lenses and spacing rings are inserted to be alternately disposed inside the hollow part and finally the lens closest to the object on the object side is pressed by the pressing ring, so that the lenses and spacing rings are disposed at predetermined positions inside the hollow part. Therefore, after the lens assembly 1 illustrated in FIG. 1 is installed in an automobile, there is a possibility that the spacing rings and the lenses disposed inside the lens assembly may sequentially move in response to movement such as vibration produced while running or shock caused by acceleration or deceleration. If the spacing rings and the lenses sequentially move, predetermined performance cannot be achieved.
In this respect, it is conceivable to fix lenses in a lens frame to the lens frame with adhesion by using the technique of Japanese Patent Application Publication No. 2006-292927. Specifically, it is conceivable to provide an adhesion part and an adhesive applied part in the barrel (lens frame) 10 having the hollow part illustrated in FIG. 1, so that each lens can be fixed by externally applying an adhesive to the adhesive applied part with a needle every time the lens is inserted. However, this makes the structure of the lens frame as well as the assembly work complicated, which is a problem. In order to simplify the structure of the lens frame and the assembly work, it is conceivable to fix the lens with adhesion to the lens frame by injecting an adhesive into a through hole formed in the lens frame.
FIG. 2 is a diagram illustrating the structure of a lens assembly 1A having a lens frame 10A provided with holes H1 and H2 into which an adhesive is to be injected.
As illustrated in FIG. 2, the hole H1 and the hole H2 are formed at positions corresponding to a lens L3 and a lens L4 of the lens frame 10A, respectively. The lens L3 and the lens L4 are fixed to the lens frame 10A with adhesion by injecting the adhesive into the hole H1 and the hole H2. This structure makes the assembly work simple, without increasing the size of the lens frame 10A.
In the structure illustrated in FIG. 2 however, there is a possibility that light may enter the lens frame 10A through the holes H1 and H2 formed in the lens frame 10A, affecting the optical performance inside the lens frame 10A.